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The Different stages of Sleep Cycle Revealed

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The Different stages of Sleep Cycle Revealed

What happens when we are asleep? What is really going on in our brain while we are catching zzz’s each night?

Quite before, say in 1950’s scientists used to believe that as people are drifted off to sleep, their brains and bodies goes into a complete ‘shutdown’ mode that allowed them to recover from the previous day. But, researchers have now learned that sleep is a whole lot more complicated than they believed. It is much more of an active state comprising of multiple distinct stages.

A typical sleep cycle lasts for about 90 minutes during which we go through four stages of sleep. The first three stages will make up for NREM (Non-rapid Eye Movement) and the fourth stage is when REM (Rapid Eye Movement) Sleep occurs.

Understanding the different stages of sleep in human will also make us aware of how sleep and sleep related disorders like obstructive sleep apnea, sleep walking etc are related to each other.

Here is everything you need to know about the different stages of sleep as to what happens inside our brain and body at each point in a sleep cycle.

Different stages of a sleep cycle

NREM- Stage 1

This is the beginning of a sleep cycle, after you have closed your eyes and decided to sleep. It is considered as a transition stage between wakefulness and sleep.

This period of sleep typically lasts for about 5 to 10 minutes, just enough to allow your body to slow down and relax. At this point, your body muscles will slow down, your eyes rolls a bit, your heart beats become regular and your blood pressure decreases. Although, you are really sleeping, you may wake up feeling like you didn’t sleep at all.

Did you know? The hypnic jerk (jolted awake when falling asleep) - mostly accompanied by the sensation of falling down happens in this stage only.

NREM- Stage 2

Things will get serious as NREM stage 2 sleep kicks in. This stage of Non-Rapid Eye Movement sleep that usually lasts for approximately 20 minutes- is characterized by decrease in body temperature, slowing down of the heart rate and the brain producing more of rhythmic waves.

Since the stage 1 and stage 2 are the ‘light sleep’ stages of NREM sleep, during the course, your body will reduce its activity to prepare you to go into a deep sleep stage. Also, it becomes harder to wake you up at this point of time.

Did you know? We spend around 45% of the total duration of our nights in this stage.

NREM- Stage 3

This stage is the merger of 2 similar stages that were separated previously (Stage 3 and stage 4). It typically lasts for 35-40 minutes after falling asleep.

This stage is the beginning of deep sleep, as the brain begins to produce deep, slow brain waves known as delta waves. There will be no eye movement and muscle activity. During this stage, people become less responsive to noises and activities in the environment.

It is during this stage, our body produces most of prolactin- a hormone that boosts our immunity system and manages inflammation. Also, the sleep during stage 3 decreases the production of stress hormone cortisol- that can otherwise cause anxiety, muscle breakdown and digestive problems. Hence it is more of a restorative sleep, when the body repairs muscles and tissues, stimulates growth and builds up energy for the next day.

Did you know? If you wake up during this NREM stage of sleep, you may feel disoriented during the first few minutes. Sleep walking tends to occur most often during this stage of deep sleep.

REM Sleep

This is the final stage of any sleep cycle and as the name indicates, during this Rapid Eye Movement sleep, your eyes will move rapidly in all directions. The first REM sleep lasts for around 10 minutes and happens after having been asleep for at least 90 minutes. As the night passes by, REM stages get longer, in fact the last stage last for an hour.

When you enter REM or Rapid eye movement sleep, your respiration and brain activity increases with the exception of heart and lungs, also the muscles of your body will become paralyzed. Muscles paralysis in REM sleep also indicates occurrence of sleep apnea or sleep suffocation. Since the patients experience complete muscle relaxation or paralysis, their airways can easily be collapsed after which it becomes difficult for them to resume to normal breathing.

Although sleep apnea can occur during any stage, it will be worst during REM sleep. Some individuals, in fact, have apnea that occurs during REM sleep only.

Did you know? REM sleep is the time when the majority of dreams occur and our legs and arms are temporarily paralyzed, perhaps to prevent us from acting our dreams.

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